1. Field of the Invention:
The present invention relates to a turret machine tool equipped with multispindle heads.
2. Description of the Background Art
One conventional turret machine tool having multispindle heads is known from Japanese laid-open patent publication No. 60-238204. As shown in FIG. 8 of the accompanying drawings, the conventional turret machine tool, generally designated by "a" has a slide table "b" mounted on a machine base (not shown) for movement toward and away from a workpiece "W". A cylindrical turret head "c" is indexably supported on an upper end of the slide table "b". The turret head "c" supports a plurality of multispindle heads "d" angularly spaced in an indexing direction. Each of the multispindle heads "d" has a pair of vertically spaced through holes "e" extending from a front end to a rear end of the multispindle head. Spindle shafts "f" extend axially through and are rotatably supported in the respective through holes "e" by bearings "g".
A machining tool "i" is replaceably mounted on the front end of each of the spindles "f" by a tool holder "h". An oil seal "j" is disposed between the front end of each of the spindles "f" and an inner wall surface of the corresponding through hole "e" for preventing foreign matter such as a cutting fluid, chips, or the like from entering the gap between the spindle "f" and the inner wall surface of the through hole "e".
Spindle gears "k" are mounted on the respective rear ends of the spindles "f". The spindle gears "k" are held in mesh with a driven gear "m" disposed substantially centrally in the rear end of the multispindle head "d" through a train of gears "n". The driven gear "m" and the gears "n" have respective gear shafts "o", "p" which are rotatably supported at their ends (left-hand ends) remote from the turret head "c" in the multispindle head "d" by respective bearings "q". The other ends (right-hand ends) of the gear shafts "o", "p" are rotatably supported in a gearcase "r" mounted on the rear end of the multispindle head "d" by respective bearings "s".
A drive gear "t" axially movably disposed in the turret head "c" can be brought into and out of mesh with the driven gear "m" of the multispindle head "d" which has been indexed. The drive gear "t" and the driven gear "m" jointly constitute a clutch mechanism for selectively transmitting rotary power from a drive mechanism to the spindles "f" and the machining tools "i".
When one of the multispindle heads "d" is indexed into the machining position confronting the workpiece "W", the turret head "c" moves toward the workpiece "W" and the drive gear "t" axially moves into mesh with the driven gear "m". Rotary power from the drive mechanism is now transmitted to the machining tools "i", which machine the workpiece "W". After the workpiece "W" has been machined, the turret head "c" is retracted away from the workpiece "W", moving the machining tools "i" away from the workpiece "W".
In the turret machine tool "a" the gearcase "r" is mounted on the rear end of each multispindle head "d" so that the opposite ends of the gear shafts "o", "p" of the gears "m", "n" are supported in the multispindle head "d" and the gearcase "r", respectively. The opposite ends of the gear shafts "o", "p" are supported in order to fully bear the machining load applied through the machining tools "i" the spindles "f" and the spindle gears "k" to the gears "n" and transmit the rotary power smoothly to the machining tools "i" when the workpiece "W" is machined.
However, since the gearcase "r" is mounted on the rear end of each multi spindle head "d", the multispindle head "d" has to be installed on the turret head "c" through the gearcase "r". Such indirect mounting of the multispindle head "d" tends to produce an installation error of the multispindle head "d", ie., to reduce the installation accuracy of the multispindle head "d" with respect to the turret head "c". The gearcase "r" also makes it inconvenient to service the gears "n" and related components.
Inasmuch as the gearcase "r" needs to have a wall thickness large enough to bear the machining load, the overall machine tool weight is large. The cost of the gearcase "r" is high because a plurality of highly accurate attachment holes for receiving the bearings "s" have to be defined in the gearcase "r".
The turret head "c" and the gearcase "r" are filled with a liquid lubricating oil for lubricating the drive gear "t" the driven gear "m" the gears "n" and the spindle gears "k". To prevent the lubricating oil from leaking out of the turret head "c" and the gearcase "r" , seal members "u" are interposed between attachment surfaces of the turret head "c" and the gearcase "r" and between attachment surfaces of the gearcase "r" and the multispindle head "d". The seal members "u" thus interposed are also responsible for lowering the installation accuracy of the multispindle head "d" with respect to the turret head "c" .
Generally, the bearings "g" by which the spindles "f" are rotatably supported in the multispindle head "d" are lubricated by grease. If the oil seals "j" are damaged or deteriorated or the pressure in the multispindle head "d" is lowered due to a reduction in the temperature therein after the spindles "f" stop rotating, then gaps are liable to develop around the oil seals "j", allowing foreign matter such as a cutting fluid, chips, or the like to enter the gaps around the spindles "f". When this happens, the viscosity of the grease decreases, tending to cause seizure of the spindles "f". If the cutting fluid, chips, or the like is mixed into the lubricating oil in the gear case "f", then the spindle gears "k" and the gears "n" will not sufficiently be lubricated. It is therefore desirable to reliably prevent such foreign matter from entering the gaps around the spindles "f".
To define two or more closely positioned holes in a workpiece, it is necessary to minimize the diameter of the spindles "f" for reducing the interaxial distance between two or more machining tools "i" which are mounted on the spindles "f". However, the spindles "f" are required to be relatively large in diameter to maintain a rigidity large enough to withstand external forces such as torsional forces that are applied to the spindles "f" while the workpiece "W" is being machined by the machining tools "i". The spindle diameter requirement poses a limitation on design efforts to reduce the distance between holes that can be machined in the workpiece "W".